Manufacture of paper containing hydroxyethyl cellulose



United States Patent MANUFACTURE OF PAPER CONTAINING HYDROXYETHYL CELLULOSE Donald Robert Erickson, Kalamazoo, Mich.

No Drawing. Application June 15, 1953, Serial No. 361,843

8 Claims. (Cl. 92-21) This application is a continuation-in-part of my application Serial No. 47,749, filed September 3, 1948, and now .abandoned, for Manufacture of Paper.

This invention relates to paper having a very high dry tear strength and particularly to such papers in which water-insoluble hydroxyethyl cellulose is employed in such .a way as to produce such a paper.

Heretofore it has been recognized that water-insoluble hydroxyethyl cellulose could be employed in connection with the manufacture of paper. its use has been suggested as a size or coating, primarily for prefabricated sheets of paper, and it has been suggested that its use would increase the wet strength of the paper. In making such paper, a solution in aqueous sodium hydroxide of water-insoluble hydroxyethyl cellulose is applied to a preformed sheet of paper. Thereafter the hydroxyethyl cellulose is precipitated in situ. This is due by using various precipitating agents which neutralize the sodium hydroxide of the aqueous sodium hydroxide solvent.

It has also been proposed that hydroxyethyl cellulose be incorporated with paper fibres in the beater and that it be precipitated and that the paper then be formed. Such paper is not materially benefited by the presence of the hydroxyethyl cellulose and does not have any improved dry tear strength.

In carrying out the present invention, hydroxyethyl cellulose is employed to produce a new sheet of paper having unusually high dry tear strength. This is accomplished by creating a temporary solution of water-insoluble hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide concentration much below that which would be required to dissolve the hydroxyethyl cellulose from solid, precipitated form.

This temporary solution is formed by adding to water a solution of water-insoluble hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide content of about to 7%. About 8 parts of hydroxyethyl cellulose would be dissolved in such aqueous sodium hydroxide.

The temporary solution is one which contains about A of 1% of sodium hydroxide. In making up the solution about 100 parts of the hydroxyethyl cellulose solution in aqueous sodium hydroxide would be added to approximately 80,000 parts of water. This would serve to suspend about 800 parts of dry cellulose fibres or other pulp.

It has been found that satisfactory results can be obtained if the amount of hydroxyethyl cellulose employed equals from /2% to 2% of the weight of the fibres. Any excess of hydroxyethyl cellulose over 2% of the weight of the fibres tends to produce a brittle sheet which does not have the desired tear characteristics.

In order to create the temporary solution of hydroxyethyl cellulose in very dilute aqueous sodium hydroxide, it is necessary to select the hydroxyethyl cellulose so as to be sure that the ethylene oxide content thereof is at least 13.5% of the cellulose content. Such hydroxyethyl cellulose is made by employing about 14% to 15% or more of ethylene oxide based upon the cellulose content of the cellulose to be etherified. The preferred product is one in which there is approximately one ethylene oxide group for each two glucose units in the cellulose. Such a product might well be termed hydroxyethyl di-cellulose. Satisfactory results will be obtained, however, if water-insoluble hydroxyethyl cellulose is employed having higher ethylene oxide content up to the pointof water solubility.

In carrying out the process, it has been found that the cellulose fibres used to form a sheet will adsorb from the temporary solution a temporary, tacky solution of hydroxyethyl cellulose which will serve as an adhesive to bind the fibres together when they are felted to form the sheet.

The adsorption of the temporary solution on the fibres is brought about by dispersing the fibres in the very dilute temporary solution and the adsorbed temporary solution will maintain its tackiness for periods adequate for the felting of the fibres together and the forming of the sheet, for instance, about minutes. Thereafter on draining of the free liquid from the felted sheet and drying the same the hydroxyethyl cellulose Will precipitate from the ,solution and will serve as a binder to bind the fibres together at their points of contact. This is brought about by the drying of the sheet for the complete removal of the water.

It has been found that most satisfactory results are obtained if the cellulose fibres are not beaten or hydrated to the extent which is commonly brought about in the beater in making ordinary paper. In carrying out the process the cellulose fibres, which are usually in the form of wood pulp, are partially dispersed in water to form a slurry. The amounts of water and the pulps used are dependent upon the freeness desired and are dictated in general by usual paper making practices.

After the slurry has been created a small amount of hydroxyethyl cellulose dissolved in aqueous sodium hydroxide is added. This creates the very dilute temporary solution which is adsorbed by the dispersed fibres.

It is possible, however, in carrying out the practice to first create the temporary solution and then add the cellulose fibres.

It has been found that in carrying out the process the hydroxyethyl cellulose tends to serve as a dispersing agent greatly facilitating the complete dispersion of the fibres and eliminating the need for the amount of beating usually employed to create the desired dispersion of the fibres in the manufacture of paper.

In carrying out the process, the addition of. the pulp to the water and the agitation of the mixture to break up lumps of pulp and to obtain fair dispersion can be carried out with very little mechanical action. The hydration resulting from this step is not substantial.

It has been found that the hyroxyethyl cellulose is removed substantially quantitatively from the temporary solution by the fibres. This is done without the use of any chemical agents and without any precipitation of the hydroxyethyl cellulose which is adsorbed as a solution on the fibres. It is there in a tacky or adhesive condition which will be maintained for sufiicient time to bring about the adhesive binding of the fibres together when the sheet is formed by felting the fibres.

As a practical matter, in carrying out this invention it is necessary to form the paper sheet promptly after the mixture of the fibres with the temporary solution of hydroxyethyl cellulose. If this is not done, the hydroxyethyl cellulose may lose its tack. The sheet should be formed within 90 minutes or the dry tear strength of the paper will be less than if the sheet were formed 7 immediately. If the mixture is allowed to stand submasses stantially more than two hours, the efiect of the hydroxyethyl cellulose is negligible.

The paper stock treated in accordance with this invention gives many practical manufacturing advantages. The stock is much freer than beaten stock and is easier to dry because the fibres are not hydrated as would be the case in fully beaten pulp. Because of this, it is possible to avoid the deteriorating effect of heat from drying and the cost is reduced and the drying process is materially speeded up.

The hydroxyethyl cellulose employed cannot be dissolved from its dry or solid state in Water. it likewise cannot be dissolved by low concentrations of aqueous sodium hydroxide. When the hydroxyethyl cellulose solution in 5% to 7% aqueous sodium hydroxide is added to the slurry of pulp or to the water, the sodium hydroxide concentration is reduced below that required for dissolution of the hydroxyethyl cellulose. However, there is then formed a temporary solution and the fibres appear to have the ability to adsorb this temporary solution, causing the tacky adhesive deposit of hydroxyethyl cellulose solution on the fibres. This temporary solution lasts for a sufficient time to carry out the steps of forming the paper after which the hydroxyethyl cellulose comes out of solution or precipitates.

As pointed out above, the preferred hydroxycthyl cel lulose is one in which the ethylene oxide content is reater than 13.5% by weight of the cellulose content of the hydroxyethyl cellulose. If the hydroxyethyl cellulose has a lower ethylene oxide content, it is not possible to make the above-described temporary solution of hydroxyethyl cellulose in the very dilute sodium hydroxide. It is therefore impossible to obtain the deposit of the tacky, temporary hydroxyethyl cellulose solution on the fibres to bind them together.

The following are examples of the practice of the invention:

Example 1 Pure sulphite pulp is added to water to give a slurry of approximately 2 /2% by weight of pulp. When the pulp has been partially dispersed by agitation but without any significant heating or hydration of the fibres, further dispersion is obtained in the partial dispersion by adding hydroxyethyl cellulose solution. The hydroxyethyl cellulose solution is one employing hydroxyethyl cellulose having an ethylene oxide content of more than 13.5% by weight of the cellulose content of the hydroxyethyl cellulose and contains 8 parts of hydroxyethyl cellulose to 100 parts of aqueous sodium hydroxide solution in which 5% is sodium hydroxide. The quantity of solution is controlled to give a quantity of hydroxyethyl cellulose equal to 2% of the dry weight of the fibres of the pulp.

The mixture is then mechanically mixed further without material beating or hydration of the pulp. The re sult of this is that the fibres of the pulp absorb a deposit of temporary solution of tacky hydroxyethyl cellulose.

Before the temporary solution of hydroxyethyl cellulose adsorbed on the fibres loses its tack or adhesive quality, the pulp slurry is passed to the paper machine. At this point or in the head box of the machine water may be added, as is conventional, so that the fibres are approximately one-half of 1% by weight ofthe slurry. The fibres are then felted into a paper sheet in a conventional manner and the free liquid is drawn therefrom. This felting operation should be carried out within an hour and a half after the addition of the hydroxyethyl cellulose in order to be sure that the hydroxyethyl cellulose remains in temporary solution and can be adsorbed in tacky form on the fibres.

The sheet formed in accordance with this example in a 37.5 pound weight will have a dry Elmendorf tear strength of from 114 to 118, whereas the same weight of paper formed without the hydroxyethyl cellulose will have a dry tear strength of approximately 66.

If the sheet is not formed until the slurry has stood for 4 about two hours, the dry tear strength will be approximately 98.5 Elmendorf.

The paper formed is particularly desirable for coating for printing. It will retain its dry tear strength even though it is subjected to temperatures as high as 1700" F. in heat-dried printing. Because the fibres have not been beaten materially or hydratedby beating, they retain substantially their full strength, which would be lost had they been beatenor hydrated materially, as is commonly done in paper making.

"Example 11 This'exa'rnple -is the'same as Example I except that bleached sulphate pulp is employed. The Elmendorf tear strength of 37.5 pound'sheets was from 135.5 to 137 on paper formed one and a half hours after addition of hydroxyethyl cellulose as opposed to an Elmendorf dry tear strength of 81 on the untreated sheet.

The sheet formed two hours after the addition of the hydroxyethyl cellulose had a dry tear of 115.5

Example III This example is the same as Example I except that the pulp consists of bleached sulphite and 45% bleached ground wood. The amount of hydroxyethyl cellulose is one-half of 1% of the dry weight of the pulp.

The dry tear Strength of paper made within an hour and a half after addition of the hydroxyethyl cellulose was 48 as opposed to a dry tear strength of 42 on a sheet formed from the same pulp in untreated condition.

Similar results are obtained if the bleached sulphite is varied from 40% to and the bleached ground wood varied from 60% to 40%.

Example I V This example is the same as Example 1 except that 15% unbleached sulphite and bleached ground wood are employed as the pulp. The percentage of hydroxyethyl cellulose is one-half of 1% of the dry weight of the pulp.

In this example the dry tear strength of the paper formed within minutes after addition of the hydroxyethyl cellulose is 14% higher than the dry tear strength of a sheet formed from the same pulp without the hydroxyethyl cellulose.

in all of the above examples the paper is formed while the fibres are coated with the tacky, temporary solution of hydroxyethyl cellulose after it is adsorbed on the fibres.

It will be understood that the present invention may be embodied in other specific forms Without departing from the spirit or essential attributes thereof. It is therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

What is claimed is:

1. The method of making paper of high dry tear strength comprising adsorbing on substantially unhydrated cellulose fibres an adhesive binder of a tacky temporary solution of Water-insoluble hydroxyethyl cellulose having an ethylene oxide content of more than 13.5% by weight of the cellulose content of said hydroxyethyl cellulose and having a total hydroxyethyl cellulose content of from /z% to 2% of the weight of said cellulose fibres by dispersing said fibres in a temporary solution of said hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide concentration below that required for dissolution of said hydroxyethyl cellulose and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and thenprecipitating the hydroxyethyl cel- 2. The method of making paper of high dry tearv strength comprising adsorbing on substantially unhydrated cellulose fibres an adhesive binder of a tacky temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of more than 13.5% by weight of the cellulose content of said hydroxyethyl cellulose and having a total hydroxyethyl cellulose content of from /2% to 2% of the weight of said cellulose fibres by dispersing said fibres in a temporary solution of said hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide concentration below that required for dissolution of said hydroxyethyl cellulose and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution whereby said fibres are adhesively secured together in said felted sheet at their point of contact.

3. The method of making paper of high dry tear strength comprising adsorbing on substantially unhydrated cellulose fibres an adhesive binder of a tacky temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of approximately 13.5% by weight of the cellulose content of said hydroxyethyl cellulose and having a total hydroxyethyl cellulose content of from /2% to 2% of the weight of said cellulose fibres by dispersing said fibres in a temporary solution of said hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide concentration below that required for dissolution of said hydroxyethyl cellulose and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution by drying said sheet whereby said fibres are adhesively secured together in said felted sheet at their point of contact.

4. The method of making paper of high dry tear strength comprising adsorbing on substantially unhydrated cellulose fibres an adhesive binder of a tacky temporary solution of Water-insoluble hydroxyethyl cellulose having an ethylene oxide content of approximately 13.5 by weight of the cellulose content of said hydroxyethyl cellulose and having a total hydroxyethyl cellulose content of from /z% to 2% of the weight of said cellulose fibres by dispersing said fibres in a temporary solution of said hydroxyethyl cellulose in aqueous sodium hydroxide having a sodium hydroxide concentration below that required for dissolution of said hydroxyethyl cellulose and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution whereby said fibres are adhesively secured together in said felted sheet at their point of contact.

5. The method of making paper of high dry tear strength comprising producing a dilute temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of more than 13.5 by weight of the cellulose content of said hydroxyethyl cellulose by adding to water a relatively small amount of a solution of said hydroxyethyl cellulose in sodium hydroxide and adsorbing on substantially unhydrated cellulose fibres from said temporary solution of hydroxyethyl cellulose a relatively more concentrated tacky temporary solution of said hydroxyethyl cellulose by suspending said cellulose fibres in said dilute temporary solution, said adsorbed temporary solution having a content of from /2% to 2% of the weight of said cellulose fibres, and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution by drying said sheet.

6. The method of making paper of high dry tear strength comprising producing a dilute temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of approximately 13.5% by weight of the cellulose content of said hydroxyethyl cellulose by adding to water a relatively small amount of a solution of said hydroxyethyl cellulose in sodium hydroxide and adsorbing on substantially unhydrated cellulose fibres from said temporary solution of hydroxyethyl cellulose a relatively more concentrated tacky temporary solution of said hydroxyethyl cellulose by suspending said cellulose fibres in said dilute temporary solution, said adsorbed temporary solution having a content of from to 2% of the Weight of said cellulose fibres, and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution by drying said sheet.

7. The method of making paper of high dry tear strength comprising producing a dilute temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of more than 13.5% by weight of the cellulose content of said hydroxyethyl cellulose by adding to water a relatively small amount of a solution of said hydroxyethyl cellulose in sodium hydroxide and adsorbing on substantially unhydrated cellulose fibres from said temporary solution of hydroxyethyl cellulose a relatively more concentrated tacky temporary solution of said hydroxyethyl cellulose by suspending said cellulose fibres in said dilute temporary solution, said adsorbed temporary solution having a content of from /z% to 2% by weight of said cellulose fibres, and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution.

8. The method of making paper of high dry tear strength comprising producing a dilute temporary solution of water-insoluble hydroxyethyl cellulose having an ethylene oxide content of approximately 13.5 by weight of the cellulose content of said hydroxyethyl cellulose by adding to water a relatively small amount of a solution of said hydroxyethyl cellulose in sodium hydroxide and adsorbing on substantially unhydrated cellulose fibres from said temporary solution of hydroxyethyl cellulose a relatively more concentrated tacky temporary solution of said hydroxyethyl cellulose by suspending said cellulose fibres in said dilute temporary solution, said adsorbed temporary solution having a content of from /2 to 2% of the weight of said cellulose fibres, and then felting said fibres into a sheet while the adsorbed temporary solution of hydroxyethyl cellulose is in a tacky condition and draining the free liquid from said felted fibres and then precipitating the hydroxyethyl cellulose from said temporary solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,863,208 Schorger June 14, 1932 2,033,481 Richter Mar. 16, 1936 2,069,763 Jones Feb. 9, 1937 2,216,845 Larson Oct. 8, 1940 2,338,602 Schur Ian. 4, 1944 2,357,962 Leeman et al Sept. 12, 1944 2,533,145 Schorger Dec. 5, 1950 FOREIGN PATENTS 301,807 Great Britain Jan. 30, 1930 462,254 Great Britain Mar. 4, 1937 

1. THE METHOD OF MAKING PAPER OF HIGH DRY TEAR STRENGTH COMPRISING ADSORBING ON SUBSTANTIALLY UNHYDRATED CELLULOSE FIBRES AND ADHESIVE BINDER OF A TACKY TEMPORARY SOLUTION OF WATER-INSOLUBLE HYDROXYETHYL CELLULOSE HAVING AN ETHYLENE OXIDE CONTENT OF MORE THAN 13.5% BY LULOSE AND HAVING A TOTAL HYDROXYETHYL CELLULOSE CONTENT OF FROM 1/2% TO 2% OF THE WEIGHT OF SAID CELLULOSE FIBERS BY DISPERSING SAID FIBRES IN A TEMPORARY SOLUTION OF SAID HYDROXYETHYL CELLULOSE IN AQUEOUS SODIUM HYDROXIDE HAVING A SODIUM HYDROXIDE CONCENTRATION BELOW THAT REQUIRED FOR DISSOLUTION OF SAID HYDROXYETHYL CELLULOSE AND THEN FELTING SAID FIBRES INTO A SHEET WHILE THE ADSORBED TEMPORARY SOLUTION OF HYDROXYETHYL CELLULOSE IS IN A TACKY CONDITION AND DRAINING THE FREE LIQUID FROM SAID FELTED FIBRES AND THEN PRECIPITATING THE HYDROXYETHYL CELLULOSE FROM SAID TEMPORARY SOLUTION BY DRYING SAID SHEET WHEREBY SAID FIBRES ARE ADHESIVELY SECURED TOGETHER IN SAID FELTED SHEET AT THEIR POINT OF CONTACT. 